ctypes: How to call unexported functions in a dll

[Coert Klaver (DT)]

Hi,

I am using ctypes in python 3 on a WXP machine

Loading a dll and using its exported functions works fine.

Now I want to use a function in the dll that is not exported.

In C this can be done by just casting the address in the dll of that
function to an apropriate function pointer and call it (you need to be
sure about the address). Can a similar thing be done directly with
ctypes?

A work around I see is writing in wrapper dll in c that loads the main
dll, exports a function that calls the unexported function in the main
dll, but I don't find that an elegant solution.

Thanks for any hint in the right direction.

BR

Coert

[Thomas Heller]

Post by Coert Klaver (DT)
Hi,
I am using ctypes in python 3 on a WXP machine
Loading a dll and using its exported functions works fine.
Now I want to use a function in the dll that is not exported.
In C this can be done by just casting the address in the dll of that
function to an apropriate function pointer and call it (you need to be
sure about the address). Can a similar thing be done directly with
ctypes?
A work around I see is writing in wrapper dll in c that loads the main
dll, exports a function that calls the unexported function in the main
dll, but I don't find that an elegant solution.

No need for a workaround.

One solution is to first create a prototype for the function by calling WINFUNCTYPE
or CFUNCTYPE, depending on the calling convention: stdcall or cdecl, then call the
prototype with the address of the dll function which will return a Python callable.
Demonstrated by the following script using GetProcAddress to get the address of

Post by Coert Klaver (DT)

from ctypes import *
dll = windll.kernel32
addr = dll.GetProcAddress(dll._handle, "GetModuleHandleA")
print hex(addr)

0x7c80b741

Post by Coert Klaver (DT)

proto = WINFUNCTYPE(c_int, c_char_p)
func = proto(addr)
func

<WinFunctionType object at 0x00AD4D50>

Post by Coert Klaver (DT)

func(None)

486539264

Post by Coert Klaver (DT)

hex(func(None))

'0x1d000000'

Post by Coert Klaver (DT)

hex(func("python24.dll"))

'0x1e000000'

Post by Coert Klaver (DT)

hex(func("python.exe"))

'0x1d000000'
Thomas